1. Technical Field of the Invention
This invention relates generally to the field of devices and methods for the specification and measurement of the perceptual intensity of one or more visual images and, more particularly, to the rapid and efficient determination of a visibility metric for such images.
2. Description of the Prior Art
Vision is the means by which most people acquire and process information about the world around them. Numerous objects intended for human use include a component of information to be identified visually by a human observer. Some everyday examples include information displayed on a screen or page, keys or buttons to be pressed on a keyboard, telephone, calculator, remote control unit, among many other examples. Therefore, it is reasonable that the design of such objects include specifications to insure that the visual information is accessible to typical human observers, that is, that the information is visible. Providing a means for measuring and specifying visibility, a “visibility metric,” is an objective of the present invention.
A significant challenge in designing standards for visibility is that such standards are based upon models of the human visual sense. However, vision is a complex and only partially understood process. Previous standards for visibility have thus tended to be complex, difficult to use and not sufficiently general to serve as a standard method or methods for the specification and measurement of visibility. The performance of various visibility metrics has been reviewed by Ahumada and coworkers in two publications: Society for Information Display, International Symposium, Digest of Technical Papers Vol. 24, pp. 305-308 (1993) and Vol. 26. pp. 45-48 (1995), the contents of both publications are incorporated herein by reference.
Other examples of visibility metrics include the work of Lubin and co-workers U.S. Pat. No. 6,654,504, US Patent Application Publication 2002/0031277 and “A Human System Model for Objective Picture Quality Measurements,” Proceedings, International Broadcasters'Convention, Amsterdam, The Netherlands, pp. 498-503 (1997). These methods developed by Lubin and co-workers require extensive calibration for each application in addition to suffering from the disadvantage of complexity. These methods are chiefly intended for image quality evaluation.
Other methods for estimating visibility include those of Barten, “The SQRI Method: A New Method for the Evaluation of Visible Resolution on a Display,” Proceedings of the Society for Information Display, Vol. 28, pp. 253-262 (1987). In addition to complexity, the Barten method suffers from the further disadvantage of being appropriate primarily for the specification of displays such as television monitors.
Standards for the measurement and specification of color are known in the art and widely used. However, such color standards typically do not address the spatial pattern employed in a visual signal (for example, the shape of a letter). Consequently, such methods are not appropriate for specifying or measuring visibility.
Thus, a need exists in the art for a standard specification and measurement of visibility, sufficiently general to be applicable to large classes of visual information but sufficiently simple for widespread implementation and use, including embedding into inexpensive systems.